Image reading apparatus and method for controlling the same

ABSTRACT

An image reading apparatus capable of reading documents includes a reading unit including a light emitting element, a mechanism configured to move the reading unit, and a control unit configured to control the reading unit and the mechanism both to carry out reading by turning on the light emitting element and moving the reading unit and to temporarily stop moving the reading unit upon occurrence of a predetermined factor. The control unit sets a first current value which is caused to flow through the light emitting element when reading is carried out and sets a second current value which is less than the first current value and which is caused to flow through the light emitting element when the reading unit is temporarily stopped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/766,462 filed on Apr. 23, 2010 (now U.S. Pat. No. 8,482,817), whichclaims priority to Japanese Patent Application No. 2009-142538 filedJun. 15, 2009. Each of U.S. patent application Ser. No. 12/766,462 andJapanese Patent Application No. 2009-142538 is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image reading apparatus, and inparticular, to an image reading apparatus configured to control opticalelements.

2. Description of the Related Art

Normally, when the temperature of a light-emitting diode (LED) generallyused in a reading unit of an image reading apparatus is increased, theluminance of the LED is decreased. When the luminance is decreased, thedensity of the read image is increased. “Japanese Patent ApplicationLaid-Open No. 2003-207860” discusses maintaining the temperature of suchLED at a constant level by arranging a temperature sensor and a heatingelement near the LED and controlling the heating element based oninformation from the temperature sensor.

During a read operation, at times, the image reading apparatustemporarily stops the read operation. For example, when the imagereading apparatus is reading a document, if a buffer memory thereinbecomes full and cannot store any more read data, the image readingapparatus temporarily stops reading the document.

If not controlled, the temperature of an LED is increased while the readoperation is temporarily stopped, and as a result, the luminance of theLED is decreased. Thus, a density difference is caused between imagesread before and after the temporary stop (after the read operation isresumed), and the border between the two images is observed as anoticeable image seam. If the technique as discussed in Japanese PatentApplication Laid-Open No. 2003-207860 is used to avoid a decrease ofsuch image quality, a temperature sensor, a heating element, and acircuit which controls these elements are required. Thus, a furtherreduction of cost is hindered.

SUMMARY OF THE INVENTION

The present invention is directed to an image reading apparatus and amethod for controlling the same. According to an aspect of the presentinvention, the image reading apparatus includes a reading unit includinga light emitting element, a mechanism configured to move the readingunit, and a control unit configured to control the reading unit and themechanism both to carry out reading by turning on the light emittingelement and moving the reading unit and to temporarily stop moving thereading unit upon occurrence of a predetermined factor. The control unitsets a first current value which is caused to flow through the lightemitting element when the reading is carried out and sets a secondcurrent value which is less than the first current value and which iscaused to flow through the light emitting element when the reading unitis temporarily stopped.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a flow chart illustrating a read operation of an image readingapparatus according to an exemplary embodiment.

FIG. 2 is a control block of an image reading apparatus according to anexemplary embodiment.

FIGS. 3A and 3B are timing diagrams illustrating a read operationaccording to a first exemplary embodiment.

FIGS. 4A and 4B illustrate configurations of light source unitsaccording to exemplary embodiments.

FIGS. 5A and 5B are timing diagrams illustrating a read operationaccording to a second exemplary embodiment.

FIG. 6 is a flow chart illustrating a current setting process in a readoperation according to the second exemplary embodiment.

FIGS. 7A and 7B illustrate configurations according to a third exemplaryembodiment.

FIGS. 8A and 8B are timing diagrams illustrating a read operationaccording to the third exemplary embodiment.

FIG. 9 is a flow chart illustrating a current setting process in a readoperation according to an exemplary embodiment.

FIGS. 10A and 10B are plan and sectional views of an image readingapparatus according to an exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 2 is a control block of an image reading apparatus 1. A readingcontrol unit 300 controls a light source unit 301 and a sensor unit 302included in a reading unit 303. The reading control unit 300 receivesinstructions from a central processing unit (CPU) 307 to control theunits 301 and 302. The CPU 307 controls operations of the image readingapparatus 1. For example, the CPU 307 moves the reading unit 303 andstores image data read by the reading unit 303 in a memory 308. The CPU307 processes commands from an operation unit 306 and controls transferof image data to a host apparatus (a personal computer (PC) 304) oraprinter (PR) 305. When the image reading apparatus is reading an imageof a document, if a buffer memory included in the memory 308 becomesfull of image data to be transferred, the CPU 307 temporarily stops theread operation by stopping the transfer of the reading unit 303 and theoperation of the sensor unit 302. When the CPU 307 determines that thebuffer memory is ready to store an enough amount of data, the CPU 307resumes the read operation.

FIG. 1 is a flow chart of an operation controlled by the CPU 307 and thereading control unit 300. The CPU 307 receives instructions to start aread operation from the operation unit 306 or the host apparatus 304. Instep S101, the reading control unit 300 turns on the light source unit301. As illustrated in FIG. 3A, the temperature of the light source unit301 is gradually increased. The reading control unit 300 includes asetting unit, and in step S102, the setting unit sets a read current. Instep S103, the reading unit 303 carries out calibration to suppressimpact caused by a variation of the light source unit 301 and the sensorunit 302.

In step S104, the light source unit 301 and the sensor unit 302 startreading an image. The sensor unit 302 reads an image line by line, andthe CPU 307 temporarily stores the read data in the memory 308. Next,the CPU 307 transfers the data to the host apparatus 304 or therecording apparatus 305. In step S105, whether to temporarily stop(suspend) the read operation is determined. If the read operation isstopped (YES in step S105), the operation proceeds to step S106. If not(NO in step S105), the operation proceeds to step S111. In step S106,the reading control unit 300 temporarily stops the operation of thesensor unit 302. In step S107, the reading control unit 300 sets acurrent value flowing through the light source unit 301 to be 12.Namely, if a certain factor arises when the reading unit is carrying outa read operation, the reading unit is stopped.

In step S108, whether to resume the reading is determined. If the readoperation is resumed (YES in step S108), the operation proceeds to stepS109. If not (NO in step S108), the operation returns to step S107. Instep S109, the reading control unit 300 amplifies (increases) thecurrent flowing through the light source unit 301. In step S110, thereading control unit 300 allows the sensor unit 302 to read an image ofone line (resumption of reading). In step S111, the number of read linesis determined. If the number of read lines has reached a preset value(YES in step S111), the operation proceeds to step S112. If not (NO instep S111), the operation returns to step S105. In step S112, thereading control unit 300 stops the operation of the light source unit301 and the sensor unit 302.

FIG. 3A illustrates temperature changes of an LED, and FIG. 3Billustrates a current value flowing through an LED set in the lightsource unit 301. Timings t1 to t13 are aligned between FIG. 3A and FIG.3B.

At timing t1, the reading unit 303 starts moving. From timings t2 to t3,the reading control unit 300 increases the current value. At timing t3,the reading control unit 300 sets a current value I1. At timing t5, thereading control unit 300 starts reading an image (start reading thefirst one line). At timing t6, the reading control unit 300 stops movingthe reading unit 303, and at timing t7, the reading control unit 300sets a current value I2. The reading control unit 300 may stop movingthe reading unit 303 and set the current value I2 at the same timing.

At timing t8, the reading control unit 300 resumes moving the readingunit 303, and at timing t9, the reading control unit 300 sets thecurrent value I1. At timing t10, the reading control unit 300 resumesreading an image. Next, at timing t11, the reading unit 303 reads animage of the last line, and at timing t12, the reading control unit 300sets the current value to be 0. From timing t8 to t10, if necessary, thereading control unit 300 carries out position adjustment control to readan image from where the reading unit 303 is temporarily stopped.

FIG. 4A illustrates a configuration of the light source unit 301. When atransistor 401 is turned on and a current I flows therethrough, a lightemitting element such as a light emitting diode (LED) 802 is turned on.A comparator 404 compares a voltage across a variable resistor 402 witha reference voltage Vref and outputs a signal that turns on/off thetransistor 401. The reading control unit 300 sets the variable resistor402 and controls on/off of the comparator 404.

For example, the reading control unit 300 sets the resistor 402 to haveresistance values R1 and R2 corresponding to the current values I1 andI2, respectively. The reading control unit 300 maintains the comparator404 in an on-state when a read operation is carried out and in anoff-state when a read operation is not carried out.

FIG. 4B illustrates another configuration of the light source unit 301.A difference between FIGS. 4A and 4B is that the resistor 407 has afixed value. The reading control unit 300 controls on/off time of thecomparator 404 based on pulse width modulation (PWM). For example, toset the above current values I1 and I2, the reading control unit 300sets on-duties corresponding to the current values I1 and I2 to be A %and B %, respectively.

FIGS. 5A and 5B are timing diagrams illustrating a read operationaccording to a second exemplary embodiment. FIG. 5A illustrates thetemperature of an LED and FIG. 5B illustrates a current value flowingthrough an LED set in the light source unit 301. Descriptions about thefeatures common between FIGS. 5A-B and 3A-B will be omitted, anddifferences between FIGS. 5A-B and 3A-B will be described.

Upon receiving a notification about a temporary stop (suspension) fromthe reading control unit 300, the CPU 307 compares an elapsed time witha threshold. Next, based on the comparison result, the CPU 307 notifiesthe reading control unit 300 of information about a current value to beset. Based on the information about the current value to be set, thereading control unit 300 sets the current value flowing through the LED.As illustrated in FIG. 7A, the CPU 307 uses a lighting counter 709arranged therein to measure the elapsed time.

In FIGS. 5A and 5B, the CPU 307 compares the elapsed time from timing t2when the LED is turned on to timing t6 when the reading unit 303 istemporarily stopped, with a time threshold Tth. At timing t7, the CPU307 controls a current value to be set. This control is carried out inthe above step S107 of FIG. 1. FIG. 6 is a flow chart illustrating acurrent value determination and setting process. In step S201, the CPU307 acquires the elapsed time. In step S202, the CPU 307 determines acurrent value to be set, based on the acquired time and the thresholdTth. If the acquired time is less than the threshold Tth (NO in stepS202), the CPU 307 sets the current value I2. If the elapsed time isgreater than the threshold Tth (YES in step S202), the CPU 307 sets thecurrent value I3 (I2<I3). Namely, based on the length of time duringwhich the LED is turned on (time that has elapsed since the LED isturned on), the current value flowing through the LED while the readingunit is stopped is determined.

Since the elapsed time from timing t2 when the LED is turned on totiming t6 when the reading unit 303 is temporarily stopped is less thanthe threshold Tth in FIG. 3B describing the first exemplary embodiment,the CPU 307 sets the current value that flows through the LED during thetemporary stop to be 12.

FIGS. 8A and 8B are timing diagrams illustrating a read operationaccording to a third exemplary embodiment. Differences between the thirdexemplary embodiment and the first and second exemplary embodiments willbe hereinafter described, and descriptions of the same features amongthe above embodiments will be omitted.

FIG. 8A illustrates the temperature of an LED, and FIG. 8B illustrates acurrent value of an LED set in the light source unit 301. Description ofthe same features among FIGS. 8A-B, 3 A-B, and 5 A-B will be omitted,and differences among FIGS. 8 A-B, 3 A-B, and 5 A-B will be described.

Upon receiving a notification about a temporary stop from the readingcontrol unit 300, the CPU 307 compares the time that has elapsed sincethe reading unit 303 is temporarily stopped with a threshold. Next,based on the comparison result, the CPU 307 notifies the reading controlunit 300 of information about a current value to be set. Based on theinformation, the reading control unit 300 sets the value of a currentflowing through the LED. As illustrated in FIG. 7B, the CPU 307 uses astop counter 710 arranged therein to measure the elapsed time.

As illustrated in FIG. 8A, at timing t24, the current value I3 is set,and until timing t25, this current value is maintained. Next, at timingt25, the current value I4 is set and until timing t26, this current ismaintained. The current value I4 is less than the current value I3.Namely, based on the time that has elapsed since the reading unit 303 isstopped, the current value to be set is determined.

This control is carried out in the above step S107 of FIG. 1. FIG. 9 isa flow chart illustrating a current value determination and settingprocess. In step S301, the CPU 307 acquires the elapsed time. In stepS302, based on the acquired time and the threshold Tth, the CPU 307determines a current value to be set. If the acquired time is less thanthe threshold Tth (NO in step S302), the CPU 307 sets the current valueI3. If the elapsed time is greater than the threshold Tth (YES in stepS302), the CPU 307 sets the current value I4 (I4<I3).

The image reading apparatus applicable to the first to third exemplaryembodiments will be hereinafter described. FIGS. 10A and 10B are planand sectional views of an image reading apparatus according to thepresent invention, respectively.

A reading unit 808 carries out a scanning operation in a sub-scanningdirection to read a document 800 placed on a document positioning glassplate 801. According to the present exemplary embodiment, at timing t5in FIGS. 5A and 5B, the reading unit 808 of FIG. 10B first reads thedocument 800 from the right end thereof and next moves to the left. Attiming t11 in FIGS. 5A and 5B, the reading unit 808 stops reading at theleft end of the document 800. When the reading unit 808 is reading thedocument 800, if a buffer memory arranged in the memory 308 becomesfull, the reading unit 808 stops moving and comes to a stop.

The reading unit 808 includes a plurality of light emitting elements 802which irradiate the document 800 with light via a light guiding member803. A sensor 804 is mounted on a sensor substrate 805 and detects thelight reflected by the document 800 via a slit 806, mirror 811, and alens 812. The plurality of light emitting elements 802 is arrayed in themain-scanning direction.

A motor 807 is a drive force which transmits driving force to thereading unit 808 via a gear 814 and a belt 815. Before a read operation,the reading unit 808 carries out calibration by using a white referencemember 810 and positioning by using an edge detection member 809.

While a configuration and control of the image reading apparatus havethus been described, the present invention is not limited thereto. Forexample, a factor to temporarily stop a read operation is not limited tothe buffer memory which becomes full. The factor may include availablememory which becomes less than a predetermined threshold. Further, thefactor is not merely limited to conditions relating to the buffermemory. For example, the factor may include occurrence of any othererror messages and instructions from users.

In the second exemplary embodiment, the current value is controlled bycomparing the elapsed time from timings t2 to t6 with the time thresholdTth. However, the current value may be controlled in another way. Forexample, the current value may be controlled by comparing the elapsedtime from timings t3 to t6 with the time threshold Tth.

Further, while an LED is used as a light emitting element in the aboveexemplary embodiments, an organic light emitting diode (OLED), which isan organic electroluminescence device, may be used as a light emittingelement.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

What is claimed is:
 1. An apparatus for controlling a reading device forreading an image by activating a light emitting element and a sensor,the apparatus comprising: a setting unit configured to set a currentvalue for activating the light emitting element to execute a readingoperation; a determining unit configured to determine that the readingoperation by the reading device is temporarily stopped; and a controlunit configured to decrease the current value set by the setting unit ina case where the determining unit determines that the reading operationby the reading device is temporarily stopped, wherein the control unitdecides the current value set by the setting unit depending on a degreeof a state of the light emitting element which is related to temperatureof the light emitting element in a case where the determining unitdetermines that the reading operation by the reading device istemporarily stopped.
 2. The apparatus according to claim 1, wherein thesetting unit sets a first current value for activating the lightemitting element to execute the reading operation and the control unitsets a second current value lower than the first current value to thesetting unit in a case where the determining unit determines that thereading operation by the reading device is temporarily stopped.
 3. Theapparatus according to claim 1, wherein the control unit increases thecurrent value set by the setting unit in a case where the temporarilystopped reading operation by the reading device is resumed.
 4. Theapparatus according to claim 1, wherein the control unit stops applyingelectrical current for activating the light emitting element in a casewhere the reading operation by the reading device is completed.
 5. Theapparatus according to claim 1, wherein the determining unit determinesthat the reading operation by the reading device is temporarily stoppedin a case where image data obtained by the reading operation by thereading device cannot be stored to a memory.
 6. The apparatus accordingto claim 1, wherein the light emitting element includes a light-emittingdiode or an organic electroluminescence device.
 7. The apparatusaccording to claim 1, further comprising a supplying unit configured tosupply image data obtained by the reading operation by the readingdevice to a computer or a printer.
 8. The apparatus according to claim1, wherein the control unit changes the current value in accordance withan elapsed time since the light emitting element is activated forstarting of the reading operation, the elapsed time corresponding to thedegree of the state of the light emitting element.
 9. The apparatusaccording to claim 1, wherein the reading device reads an image on adocument by using a line type of a reading unit which comprises thelight emitting element and the sensor, and the control unit causes thereading device to perform a relative scanning between the reading unitand the document.
 10. The apparatus according to claim 9, wherein thecontrol unit causes the reading device to perform the relative scanningby moving the reading unit.
 11. A method of controlling a reading devicefor reading an image by activating a light emitting element and asensor, the method comprising: setting a current value for activatingthe light emitting element to execute a reading operation; determiningthat the reading operation by the reading device is temporarily stopped;and decreasing the set current value in a case where it is determinedthat the reading operation by the reading device is temporarily stopped,wherein the set current value is decided depending on a degree of astate of the light emitting element which is related to temperature ofthe light emitting element in a case where it is determined that thereading operation by the reading device is temporarily stopped.
 12. Themethod according to claim 11, wherein the set current value foractivating the light emitting element to execute the reading operationis a first current value and a second current value lower than the firstcurrent value is set as a decreased current value in a case where it isdetermined that the reading operation by the reading device istemporarily stopped.
 13. The method according to claim 11, furthercomprising increasing the set current value in a case where thetemporarily stopped reading operation by the reading device is resumed.14. The method according to claim 11, further comprising stoppingapplying electrical current for activating the light emitting element ina case where the reading operation by the reading device is completed.15. The method according to claim 11, wherein it is determined that thereading operation by the reading device is temporarily stopped in a casewhere image data obtained by the reading operation by the reading devicecannot be stored to a memory.
 16. The method according to claim 11,wherein the light emitting element includes a light-emitting diode or anorganic electroluminescence device.
 17. The method according to claim11, further comprising supplying image data obtained by the readingoperation by the reading device to a computer or a printer.
 18. Themethod according to claim 11, wherein the set current value is changedin accordance with an elapsed time since the light emitting element isactivated for starting of the reading operation, the elapsed timecorresponding to the degree of the state of the light emitting element.19. The method according to claim 11, wherein the reading device readsan image on a document by using a line type of a reading unit whichcomprises the light emitting element and the sensor, and performs arelative scanning between the reading unit and the document.
 20. Themethod according to claim 19, wherein the reading device performs therelative scanning by moving the reading unit.